1. Field of the Invention
The present invention relates to a keyphone terminal of a keyphone system and, more particularly, to a method of selectively connecting a telephone call by retrieving a calling party's number corresponding to a waiting call which is received during the telephone call over a central office line.
2. Description of the Related Art
In a conventional keyphone system, when a called party at one extension receives calls through a plurality of central office lines or from another extension, telephone call service is provided only to the central office line which called first, and the other central office lines are placed in a waiting state until the first telephone call ends. Accordingly, the called party would have no way of knowing whether one or more of the waiting calls was more important than any other call, and the waiting calls could only be answered in the order received.
A well known feature in the art is the transmission of caller identification information or calling line information when a telephone call is made. Such information is useful for a variety of reasons, one of which is to provide a calling party's telephone number to a called party so that the called party can determine whether to answer the call or not. Transmission of caller identification information and calling line information is described, for example, in U.S. Pat. No. 5,550,905 to David P. Silverman entitled Method And Apparatus For Delivering Calls And Caller Identification Information To Multi-Line Users and U.S. Pat. No. 5,479,493 to Albert D. Baker, et al. entitled Calling Line Identification Adjunct For Use With A Communication System, incorporated by reference herein.